1. Field of the Invention
The present invention relates to methods and apparatus for feeding back channel quality indication in a communication system.
2. Description of the Related Art
This application, pursuant to 37 C.F.R. §1.57, incorporates by reference the following publications:
[1] 3GPP R1-075037, “Draft Change Request to TS 36.212 v8.0.0”;
[2] 3GPP R1-075069, “Summary of AH session on AI 6.4.5 “UE Procedures for downlink shared channel””, Samsung;
[3] “[LTE] CQI table construction”, email discussions on 3GPP RANI email reflector.
Table 1 shows an example of a channel quality indication (CQI) table. Each CQI index of the table represents the channel condition estimated by a mobile station (i.e., User Equipment or UE). For a given channel condition, the most appropriate CQI index is selected and fed back by the mobile station. As an example, as shown in Table 1, if CQI index 9 is reported, the UE recommends modulation and coding scheme (MCS) as quadrature phase-shift keying (QPSK), ¼ code rate ( 64/256=¼). Note that this recommendation only serves as an input for the base station (i.e., Node B) to make a scheduling decision. The Node B may or may not follow the recommendation by the UE. Also note that there are various ways of constructing the table. For example, the table may be constructed with a subset of the columns as shown in Table 1. As an example, the table may consist of the CQI index column, the modulation column, and the code rate column. Or, alternatively, the table may consist of the CQI index column, the nominal transport block size (TBS) column, and (optionally) the modulation column.
TABLE 1An example of CQI tableNominalCQIspectralNominalindexModulationCode Rate × 256efficiencyTBS0N/AN/AN/AN/A1QPSK100.078125402QPSK130.1015625483QPSK160.125644QPSK200.15625725QPSK260.203125966QPSK320.251207QPSK400.31251528QPSK510.39843751929QPSK640.524010QPSK830.648437531211QPSK1000.7812537612QPSK1200.937544813QPSK1401.0937552814QPSK1611.25781256081516QAM841.31256241616QAM1001.56257521716QAM1151.7968758641816QAM1312.0468759761916QAM1472.29687510882016QAM1632.54687512162116QAM1812.82812513442216QAM1993.10937515042364QAM1383.23437515682464QAM1513.539062516962564QAM1653.867187518562664QAM1794.195312520162764QAM1944.54687521762864QAM2094.898437523682964QAM2215.179687524963064QAM2315.414062526243164QAM2365.531252688
Contemporarily, when a UE feeds back a CQI index selected from Table 1, the UE has to use 5 bits for the CQI index, which creates a large overhead for the control signal.